Planar display devices, represented by a liquid crystal display (LCD) device (LCD), have been utilized in a variety of fields through use of their characteristics of being lightweight, small in thickness and low in consumption power. Among them, liquid crystal display devices are in wide use for information equipment and AV equipment represented by a personal computer and a television.
Further, display devices where a self-light-emitting element is used for a displaying part, such as an electroluminescence-type electroluminescence (EL) display device and electronic paper making use of reflected light, have come to be used as next-generation thin display devices. The EL display device has characteristics such as a wide viewing angle, a high contrast, and rapid responses adaptable to moving images. The electronic paper is characterized by low power consumption which is obtained due to its memory function and reflective performance.
It has hitherto been required for such display devices to have reduced thickness and weight. Further, for example in the case of being mounted in a train, a car and the like, it is required to display a large amount of information with high efficiency and visibility in a limited space. Moreover, it is required to be fitted for a design of mounting equipment or an installation location.
In response to such requirements, studies and developments have been conducted on a curved display obtained by forming a display surface into a curved form so as to be integrated with an external form of a casing.
Realization of the display in a curved form requires the substrate of the display panel to have flexibility. As an example of such a substrate, for example, a plastic substrate (i.e. resin substrate) is known. In the case of a liquid crystal display, for example, an active element (TFT etc.), wiring and the like are formed on one resin substrate, and a color filter, a black matrix and the like are formed on the other resin substrate. For formation of these various elements, there are adapted a film formation step of forming a metal thin film and a semiconductor layer, and a photolithography step of forming a fine pattern. However, with these steps including a heating step at not lower than 200° C., a chemical treatment step and the like, heat resistance, expansion and shrinkage of the resin substrate become problems.
Meanwhile, a glass substrate has been widely used for the liquid crystal display and the like. The glass substrate has a small expansion coefficient, and excellent heat resistance and chemical resistance. However, the glass substrate has a problem of being hard and apt to break, and has thus been regarded as inappropriate for the display in the curved form. As opposed to this, it is proposed that a glass substrate with a thickness not larger than the degree of 0.2 mm can be made flexible and curved (cf. Japanese Patent Application Laid-Open No. 2004-46115). It is to be noted that a typical thickness of the glass substrate used for the liquid crystal display is, for example, from 0.5 to 1.0 mm.